The internal combustion engine, widely used for over 100 years, is by far the most powerful and efficient machine in wide use for generating power and transferring it to a powered element. The internal combustion engine in widest use today is a reciprocating piston engine formed from one or more pistons, each of which is housed in a dedicated cylinder and which reciprocates back and forth in compression and expansion strokes to compress an air-fuel mixture and to generate power upon ignition of the fuel in that mixture. So-called two-stroke engines operate through both a compression stroke and an expansion stroke in each single 360° cycle of piston motion. In so-called four stroke engines, on the other hand, the intake and exhaust strokes in each cylinder are separated from one another by compression and expansion strokes. The engine therefore undergoes a combustion event only during every other cycle of piston movement.
Both types of engines, though highly powerful, suffer the disadvantage of requiring dramatic changes in momentum as the pistons accelerate, decelerate, change direction, and then reaccelerate and decelerate. These changes dramatically reduce the efficiency that could otherwise be achieved by an internal combustion engine, resulting in a reduction of the power-to-weight ratio of the engine. They also induce considerable stress on the engine's components. They also induce vibrations in the engine that induce additional stresses on engine components and accelerate wear. The engine components must be oversized to accommodate the stresses imposed on the engine, further reducing the power-to-weight ratio achievable by the engine.
In order to overcome these disadvantages, rotary engines were developed that were characterized by the powered element taking the form of a rotating rotor as opposed to a reciprocating piston. The best known and most commercially successful such engine is the so-called Wankel engine, which has a three-sided rotor turning on an eccentric shaft. The engine fires once every revolution of the eccentric shaft, so a single rotor is in some ways equivalent to a two-cylinder, four stroke reciprocating engine. The engine produces 12 “strokes” per revolution. A rotary engine of this type is mechanically much simpler than a reciprocating piston engine and is subjected to fewer vibrations. Since it is not subject to the inertia-induced stresses and vibration-induced stresses of a reciprocating piston engine, its components can be considerably less massive, and it therefore has higher power-to-weight ratios than a reciprocating piston engine of comparable output.
However, Wankel and similar rotary engines experienced severe sealing problems due to the fact that a multiple cavity rotor rotates in a cylindrical chamber. They are also prone to flooding problems not experienced by reciprocating piston engines. These and other problems reduced the durability and reliability of the Wankel engine, limiting its commercial success to applications such as high-performance vehicle engines where neither efficiency nor long life were significant considerations.
The need therefore remains for a mechanically simple internal combustion engine having a higher power-to-weight ratio than traditional reciprocating piston engines.
The need also exists for a rotary engine lacking the sealing problems and other problems associated with earlier-known rotary engines.